Conventional high-capacity multi-wavelength optical networks have been operated in the past with fixed frequency spacing between optical channels, typically in a range of 25 GHz to 100 GHz. Multiplexing of channels within such a conventional high-capacity multi-wavelength optical network has usually been undertaken with multiplexers based on fixed-grid optical components such as Arrayed WaveGuide Gratings AWG or Thin Film Filters TFF. A smaller, more narrow channel spacing increases the number of wavelengths available in the optical amplification frequency bands which can have a direct impact on the overall fiber capacity for a given modulation rate per wavelength. Evolution in optical transceiver technology is now resulting in a higher modulation rate capability which requires greater channel passband, and thus channel spacing. Consequently, there has been much interest in flexible grid or flexgrid multiplexing which enables a mixture of channel spacing in the same optical fiber and which allows a mix of modulation rates to achieve a greater fiber capacity than a conventional fixed-grid optical network. A flexgrid optical system also enables groups of channels, or superchannels, to be transported as a single entity without optical filtering between individual channels. This enables channels within the superchannel to be packed closer together without wasting any optical spectrum. However, conventional flexgrid optical systems using superchannels do not account for variations of impairments within a superchannel with multiple transceivers. Individual wavelength paths within a superchannel may vary by several decibels which requires a specification for a worst case and consequently the frequency spectrum usage cannot be optimized.
Accordingly, there is a need to provide a method and apparatus for managing a frequency spectrum in a wavelength division multiplexing, WDM, network where the use of the frequency spectrum is further improved.